Purpose: :
Cells from tumors like retinoblastoma are suspected to havetwo kinds of cell populations, one being quiescent stem likecells, and another dividing cells. In order to investigate andquantify the populations, we studied the human Rb cell lineY79 for their clone forming ability, differential gene expressionand cell cycle status.

Methods: :
Y79 cell line was maintained in RPMI with 10% FCS. Single cellassay was performed to evaluate clone-forming ability. One millioncells were stained and analyzed for CD133 by Flow cytometryand sorted for CD133+/CD133- populations. These two subpopulationswere then evaluated for cell cycle status by propidium iodidelabeling, and differential expression of putative stem/progenitorcell markers ABCG2, PROX1 by RT-PCR.

Results: :
Clone forming ability was noted in 26.6±3.8% cells andCD133 expression in 79.7±1.3% of the cells. RT-PCR analysisof the CD133- population showed the expression of PROX1, whichwas not detected in the CD133+ cells. Majority of CD133- population(83.3±4.1%) were in G0/G1 phase, while CD133+ cells werepredominantly (81.1±10.6%) in S, G2/M phase as assessedby PI staining.

Conclusions: :
The Y79 cell line showed presence of cells with clone- formingability and differential expression of CD133, thus supportingthe existence of putative stem-like cells. Expression of PROX1and quiescence of CD133- cells, further substantiate this hypothesis.